It is known to dispense liquid products from a dispenser such as an aerosol can, or a garden sprayer apparatus and the like, by internal pressure that forces the product out through a nozzle when a valve is manually actuated. It has been found desirable to generate the pressure by means of a confined chemical reaction that causes gas to be produced within the dispenser without the reactants coming into contact with the product to be dispensed and without release of the reactants to the atmosphere by enclosing the gas-producing chemicals or reactants within a flexible barrier-bag or pouch. Initially, the space occupied by the pouch containing the gas-producing chemicals is only a relatively small part of the total inner volume of the dispenser; the larger part of the dispenser volume is used to hold the product that is to be dispensed. The gas produced by the chemical reaction exerts outward pressure on the flexible bag and thus indirectly on the product to force the product out of the dispenser during use in successive amounts until substantially all of the product is ultimately dispensed.
The quantities of gas-forming materials put into the dispenser initially are determined by the volume of gas that must be produced to expel substantially all of the product with at least a minimum residual pressure for the final quantity to be dispensed, but if the total stoichiometric amounts of these materials are brought together initially so that they can react and produce the gas before any of the product has been dispensed, the initial pressure within the dispenser would be undesirably high. As the product is dispensed under such circumstances, the pressure will gradually decrease and rather than be constant having the pressure too high initially imposes structural requirements on the outer container and involves safety hazards.
In U.S. Pat. No. 3,718,236, the barrier is an inflatable pouch, and it is proposed not to generate all of the gas at once but to generate it in fractional quantities so that only enough pressure will be generated at each stage to inflate the pouch an additional fractional amount, starting with little or no inflation and ending with the pouch virtually filling the dispenser to supplant the product as the product is dispensed. This arrangement makes it possible to generate as much pressure as is needed at any time to dispense the product at a relatively constant rate and keeps the dispensing pressure relatively constant.
Generation of the gas in fractional quantities in the aforesaid patent is accomplished by sealing gas-impermeable walls into the pouch to divide the pouch into a series of chambers. A predetermined portion of at least one of the gas-forming chemical reagents is placed in each chamber as the pouch is being produced, and both reagents and a solvent are placed in the pouch as start-up components for the gas-forming reaction. At least one of the necessary start-up components is separated from the others by encapsulation in a water-soluble coating to prevent the reaction from starting until after the time of sealing the dispenser. Thereafter, as the valve is actuated to open the dispensing orifice, the gas in the pouch expands, expelling some of the product through the orifice. The walls that separate the pouch into chambers can stretch to only a limited extent, and the quantity of at least one of the reagents in the first chamber is limited in amount so that the reaction of that reagent with the other in solution in the pouch will produce only slightly more than enough gas to expand the first chamber fully and to rupture the wall that separates the first and second chambers. This permits admixture of the additional material in the second chamber with the remainder of the solution in the pouch to produce a little more than enough additional gas to expand the combined first and second chambers fully (as enough of the product is dispensed to make that expansion possible) and to rupture the wall separating the second and third chambers. The process is continued, with the formation of successive quantities of gas and expulsion of the product until all of the product has been expelled. The pressure thus generated in the pouch is less than the maximum that would have been generated initially, if the same total quantities of reagents had been mixed all at once, yet the operating pressure provided is still ample.
Typical reagents that have been found to be quite satisfactory are sodium bicarbonate and citric acid which, when mixed in an aqueous solution, produce carbon dioxide. Other reagents can be used instead, such as dilute hydrochloric acid (e.g. 10-30% or even up to about 35%) in place of citric acid, and lithium carbonate or calcium carbonate in place of sodium bicarbonate.
Carbon dioxide is not a dangerous gas in the quantities generated within a typical dispenser, so that even if the dispenser were crushed, the gas forming materials, either before or after the gas-forming reaction, would not be considered toxic or dangerous.
One of the requirements of the structure shown in U.S. Pat. No. 3,718,236 is that the rupturable walls must be attached in a gas-tight manner to the flexible, but stronger, outer walls of the pouch or the barrier that separates the gas-forming reaction from the product to be dispensed. Not only must the rupturable walls be properly attached, but a proper quantity of the selected reagent must be placed within each chamber before the wall to that chamber is sealed. Furthermore, it is desirable to carry out the sealing in such a way that little or no air is trapped within each chamber during manufacture. Any trapped air would displace some of the initial product, and might cause the dispenser to contain less of the desired product than it should contain.
An improved pouch to be inserted in a dispenser is described in U.S. Pat. No. 4,360,131. The pouch disclosed therein does not have individual walls to separate the interior of the pouch into chambers. Instead, an insert containing the small, additional quantities of one of the reagents is placed in the pouch and attached to the flexible walls thereof just before the final assembly of the pouch and of the dispenser. The insert consists of two sheets of plastic smaller in dimension than the pouch. One of the sheets has one or more rows of recesses formed in it. The one reagent is placed in each of these recesses during manufacture of the insert and a second sheet is sealed to the first sheet to keep water, or more particularly, an aqueous solution of the other chemical reagent from reaching the reagent in the recesses. Furthermore, the sealing is arranged at different spaced locations from each of the recesses so that the two sheets can be peeled apart in such a way that the contents of each newly opened recess can admix in sequence with the solution containing the other reagent.
In order to allow the peeling action to take place, one side of the insert is sealed to the inside of the pouch and the other side of the insert is sealed to the opposite inner surface of the pouch. Gas generated within the pouch forces these two opposed parts of the pouch to spread farther and farther apart, to the extent permitted by expulsion of the product being dispensed, thereby peeling the sheets of the insert apart and giving access in a series of steps to the recesses containing the necessary reagent to continue the gas forming reaction. Thus, like the structure in U.S. Pat. No. 3,718,236, the structure in U.S. Pat. No. 4,360,131 allows the chemical reaction to take place in a succession of steps and not all at once, thereby controlling the gas pressure at a relatively constant level.
In using such peelable inserts, it is necessary to place the insert in the pouch, together with the starting solution of an initial quantity of one reagent and a dissolvable or rupturable capsule containing the other reagent, just before the pouch is sealed and just before the dispenser is filled and completed. As a result, it is necessary to provide sealing apparatus at the point of assembly of the dispenser and it is also necessary to be certain that the final manufacturing steps can be carried out in a short time interval before the gas-forming process gets started.
U.S Pat. No. 4,376,500 discloses a further improved version in which one wall of the pouch has recesses formed in it to receive small quantities of one of the reagents. These recesses are sealed, after the reagent had been placed therein, by a small sheet affixed in a manner similar to that described for the insert in U.S. Pat. No. 4,360,131. During expansion of the pouch in use within the dispenser, the small sheet is simply peeled back from the main wall in which the recesses are formed. The starting chemicals, one of them possibly in the form of a powder and capsules containing the other, are placed on one of the pouch outer sheets during assembly, and water is placed in a rupturable container, either as a separate small container to be enclosed within the pouch during manufacture or in a vacuum-formed recess in the same sheet with the other smaller recesses, but to be covered by a rupturable membrane. In either instance, the water is released by rupturing its container, or its cover, just prior to insertion of the pouch in a dispenser. Start-up chemical reaction is delayed until such time as the water has dissolved the powdered, loose reagent and the capsule containing the other reagent to allow the reagents to react and generate gas. From that point on, the peeling back of the small sheet to expose successive quantities of the reagent in the small recesses proceeds as in U.S. Pat. No. 4,360,131.
In the manufacture of any of the foregoing structures, the handling of the reagents must be carefully controlled. Using them in capsule form adds to the costs because of the expense of the capsules. Different start-up pressures are required to dispense different products from different dispensers, and this requires the availability of a large inventory of combinations of capsules of different size or different content of one of the reagents. In addition, using one of the chemicals in powder form during the assembly of the pouch structure may cause excessive dust in the assembly plant. Furthermore, it is desirable to be able to control, fairly accurately, the length of time between initiation of the start-up reaction and the time the reaction itself begins to cause gas to be formed.